Direct current voltage amplifier



May 15, 1945 w. M. ROBERDS ET A1. 2,375,948

DIRECT CURRENT VOLTAGE AMPLIFIER Tlc l Filed March 24, 1943 E? www,

ATT'ORNFY Patented May i5, i945- rss' PATENT OFFICE DIRECT CURRENT VOLTAGE LIFIER of Delaware Application March 24, 1943, Serial No. 480,290

Claims.

The present invention relates to thermionic ampliers and more particularly to an amplier system utilizing a cathode-ray or beam deection tube capable of amplifying small D. C. voltages.

It is one of the objects of our invention to provide an electronic amplifier which is provided with a low impedance input, which is extremely sensitive, and which develops a large output voltage with respect to its input voltage.

Another object of the invention is to effect the control of the electron stream in an electron discharge tube amplier by means of a magnetic eld.

Still anotherv object of the invention is to cause the deflection of the cathode-ray beam produced in the tube to be controlled by the input voltage.

A further object is to pick up D. C. energy at a low voltage from a low impedance circuit and to put it out at a high impedance level whereby further ampliiication by ordinary electronic tubes is eiiciently carried out.

A better understanding of our invention will be obtained and other objects, features and advantages will appear from the following description taken in connection with the accompanying drawing in which Fig. 1 illustrates schematically a circuit in accordance with the invention for amplifying small D. C. voltages, the magnetizing coils being external of the tube and shown for clarity as displaced through an angle of 90 degrees from their actual location; Fig. 2a is a plan view, partly in section, of the beam-deflection tube of Fig. 1, with the magnetizing coils shown in their proper location; Fig. 2b is a view similar to Fig. 2li but with the magnetizing coils contained within the tube envelope; Figs. 3a and 3b are views showing diagrammatically the deflection of the cathode-ray beam or electron stream with varying input control voltages.

Referring to Fig. l there is shown in crosssection an electron discharge tube I of the beam deflection type, comprising an evacuated receptacle 2 within which there is contained a metallic cylinder 3 suitably supported from the base end of the receptacle. The cylinder is closed at opposite ends by circular disc electrodes 4 and 5. A third circular disc electrode 6 is interposed between the latter disc electrodes but positioned closer to the electrode 5. The electrodes 4 to 6 are each provided with a slitted aperture 'l substantially of the form shown in Fig. 2a, the several apertures being in alignment as shown. A cathode or electron emitter 8 of the indirectly heated type is positioned externally of the cylinder 3 and close to the aperture of the electrode 55 5, and an anode or electron collector 9 is positioned externally and adjacent the aperture of electrode 4. In the space between the disc electrodes 4 and 6 and on opposite sides of a median line passing through the electrode apertures are a pair of static deecting plates I0 and II disposed in parallel relation. The cathode 8 and the apertured electrodes 5 and 6 constitute an electron gun which as is well known produces a thin ribbon-like electron beam which passes between the deflecting plates I 0 and II and through the apertured electrode 4 and finally impinges upon the anode or collecting electrode 9.

For connection to external circuit elements, individual lead-in conductors 8', 9', Ill and II are provided respectively for the cathode, the anode and the static deecting plates. The apertured electrodes 4, 5 and 6 and the metallic cylinder 3 to which they are conductively connected are provided with a common lead-in conductor 3' which is connected to the positive terminal of a suitable source of power supply, such as the battery I2. 'Ihe cathode return or lead-in conductor 8' is connected to the negative terminal of the source I2, and the delectingl electrode leads I0 and II which pass through suitable apertures in the cylinder 3 and through the side Wall of the tube envelope 2 are connected to variable taps on the potentiometers I3 and I4 respectively.

' A pair of magnetizing coils I5 and I6, which vmay be located outside the tube `receptacle as shown in Fig. 2a or Within the receptacle as shown in Fig. 2b, are* disposed in parallel relal tion and laterally with respect to the tube axis. The coils are so wound and electrically connected that their magnetic elds are in phase, that is in the same direction, and at right angles to the direction of travel of the electron beam. Since electrons are deected at right anglesto the magnetic field through which they pass, as viewed in the drawing the electron beam will be deflected in a direction transverse to the slit in electrode 4. The Voltage to be controlled and amplified is connected to a pair of terminals` designated input to which the magnetlzing coils are connected.

The anode or collecting electrode 9 is connected through a pair of load resistors Il, I8 to the power supply source at a point which is lower in potential by about 45 volts than that applied to the apertured electrodes 4 to 6. The high potential or anode end of the resistor I1 is connected to the control grid of a power amplier tube 2U, and the low potential end of the resistor I8 is connected to the control grid of a second tive .bias for power tube 2l. The battery 22 or other known means may be utilized to provide a suitable negathe grids of tubes 20, 2l. The resistors 23, 24, -25 are connected between the plates of the power tubes and constitute the output load therefor. A suitable source of power supply 26 is connected between the cathodes and the resistor 24, the connection to the latter being adjustable in order that the anodes of the tubes 20 and 2l may have equal voltages impressed thereon. The amplified' voltages are derived from the terminals which are designated output and to which may be connected a meter or other indicating device.

In the operation of the circuit above described, by means of the potentiometers I3 and I4 the voltage across the static deection plates I and II is adjusted until the electron beam is on the very edge of the slit in electrode 4, as shown in Fig. 3a. A very small D. C. current flowing in the magnetic deflection coils I5 and I6 will produce a magnetic eld, the extent of which at right angles to its direction is substantially that shown by the dotted circle, and will deflect the beam further into the slit as shown in Fig. 3b. This beam of electrons, having fallen through a potential difference of nearly 300 volts, passes electrode 4 and goes on to strike anode 9 in spite of the retarding potential of 45 volts between electrodes 9 and 4. The beam strikes `9 hard enough to knock out showers of secondaryA electrons. These secondaries, once freed from their parent electrode are drawn to the more positive electrode 4.

The electrons passing from 9 to 4 constitute an electric current which returns to 9 via the portion 21.0f the battery I2 and the resistors I8 and I'I. Thus when this current is owing, the grid of tube 2| is made negative with respect to its cathode and the grid of tube 20 is made positive with respect to its cathode. Therefore the plate current of 2D is'increased and that of 2| is decreased. This unbalance of currents appears in the output meter and hence the reading of an output meter connected to the output terminals is dependent upon the current which flows in the coils I5 and I6. Over an appreciable range the output current is substantially proportional to the input current. f

In connection with high frequency heating and surface hardening of steel it is desired to get a graphic record of the temperature changes in the surface layers as the power is applied. Small thermo-couples will respond to such temperature changes but since the times of heating and coolingvare in the order of a few'tenths of a second it is difiicult to obtain a recording instrument which would be fast enough in its response and still give readable deflections for the voltages developed by the thermo-couples. Several types of ampliers and recording instruments were considered but all seemed rather clumsy or unduly complicated.

In one application of the present invention a thermo-couple was connected to the input terminals leading to the magnetizing coils, and the small D. C. potential generated by the thermocouple was amplified a thousand fold. The thermo-couple, being a low impedance device cannot be coupled efficiently to the control grid of a conventional amplifier tube neither directly, because of the great difference in impedance of the two circuits and because contact potentials in a thermionic grid circuit are of the same order of magnitude as the thermal E. M. F.s, nor

indirectly through a transformer since the thermo-couple voltages are D. C. However by connecting a thermo-couple or other low impedance source to the low impedance magnetizing coils the resulting current will cause magnetic elds sufficiently large to deect the electron stream of the beam deflection tube in the manner explained above and thus eiciently control the voltage in the output circuit of that tube. From this output circuit (which is of high impedance) it is easy to couple efficiently to further stages of amplification in the conventional manner.

The combined resistance of the coils, each of '75 turns of No. 22 copper Wire, was about the same as that of the thermo-couple so that the magnetic effect of the comparatively large currents flowing in the coils is capable of being used to measure the E. M. F.s developed by the thermocouple. A

While we have shown and described a preferred embodiment of our invention, it will be understood that various modifications and changes will occur to those skilled in the art without departing from the spirit and scope of this invention. We therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim is:

1. A circuit for the amplification of small D. C. voltages comprising a pair of input terminals to which the D. C. voltages to be amplied are applied, an electron discharge tube provided with a plurality of electrodes constituting an electron gun for producing an electron beam, an anode and an apertured electrode positioned in front of the anode, a first means adapted in the absence of an input voltage to deflect the electron beam so that it impinges substantially entirely on the apertured electrode, a second means connected to the input terminals and responsive to input voltages impressed thereon for deiiecting the electron beam so that varying amounts of the electrons are caused to impinge on the anode, and a circuit including a utilization device connected to the anode.

2. A circuit in accordance with the invention defined in claim 1 wherein the second beam deecting means is disposed externally of the tube.

3. A circuit in accordance with the invention defined in claim 1 wherein the second beam deflecting means is disposed within the tube.

, 4. A circuit for the amplification of small D. C.

voltages comprising a pair of input terminals to which the D. C. voltages to be amplified are applied an electron discharge tube provided with a plurality of electrodes constituting an electron gun for producing an electron beam, an anode and an apertured electrode positioned in front of the anode, means adapted in the absence of an input voltage to deilect the electron beam so that it impinges substantially entirely on the apertured electrode. magnetic means connected to the input terminals and responsive to the input voltages impressed thereon arranged to produce a magnetic eld at right angles to the eleotron beam and for deflecting the electron beam so that varying amounts of the electrons are caused to impinge on the anode, and a circuit including a utilization device connected tothe anode.

5. A circuit for obtaining high amplification of small D. C. voltages comprisingy a pair of input terminals to which the D. C. voltages to be amplied are applied an electron discharge tube provided with a cathode, an anodey and a plurality of apertured electrodes interposed therebetween, said cathode and certain of the apertured electrodes constituting an electron gun for producing an electron beam between cathode and anode,

a, rst means adapted in the absence of an input voltage to deect the electron beam so that it impinges substantially entirely on the aper-l tured electrode, a. second means connected to the impressed thereon for input terminals and responsive to inputvoltages delecting the electron beam so that varying cross-sectional areas of the electron beam are caused to impinge on the anode, and a circuit including a load connected between the anode and cathode.

WESLEY M. ROBERDS.

BENJAMIN F. WHEELER. 

